This is pretty obvious, but scientists are finding more details about why. The two conclusions are first, that people were sicker over a hundred years ago than was generally known due to diet, environment and lack of medical treatment. Second, that the health of the mother while pregnant and of the child before age two carries important long term health benefits.
NYT - So Big and Healthy Grandpa Wouldn’t Even Know You
The Keller family illustrates what may prove to be one of the most striking shifts in human existence — a change from small, relatively weak and sickly people to humans who are so big and robust that their ancestors seem almost unrecognizable.
New research from around the world has begun to reveal a picture of humans today that is so different from what it was in the past that scientists say they are startled. Over the past 100 years, says one researcher, Robert W. Fogel of the University of Chicago, humans in the industrialized world have undergone “a form of evolution that is unique not only to humankind, but unique among the 7,000 or so generations of humans who have ever inhabited the earth.”